Multi-range tunable oscillator



Dec'. 28,1937.

l.. R. KIRKwooD MULTIRANGE TUNABLE oscILLAToR- Filed June 50, 1936 2Sheets-Sheet l '5MM/marasma Fa? G @nA/0 Dec. 28, 1937.

l.. R.A AKIRKwooD MULTIRANGE TUNABLE OSCILLATOR 2 Sheets-Sheet 2 FiledJune 50, 1936 Patented Dec. 28, 1937 UNITED STATES PATENT OFFIQE2,103,853 MULTI-RANGE TUNABLE OSCILLATOR tion of Delaware ApplicationJune 30, 1936, Serial No. 88,175

12 Claims.

operation such as operation over a plurality of wide frequency ranges ina multi-Wave band receiver, it has been found to be diflicult to provideuniform operation and output from the oscillator.-

One difficulty encountered in the design and operation of a multi-rangeoscillator lies in the fact that in any wave band or frequency range afixed degree of feed back vcoupling may cause instability of operationat the high frequency end o of each wave band or tuning range.

It is, therefore, an object of the present invention to provide anoscillator for low power signalling apparatus and the like such as abattery receiver, in which strong oscillations'are generatedsubstantially uniformly throughout each frequency band and in aplurality of frequency bands without instability of operation in thehigh frequency end of any tuning range.

The range of operation contemplated in connection with circuitsembodying the invention -may include a total range of from 1,000 to25,000 k. c., for example, in a series of three bands, each band tunableby arvari'able capacitor or the like in conjunction with suitable tuninginductances changeable by switching means for each band.

In providingA a simplified oscillator system wherein strong oscillationsare produced with low voltage power sources, it is also a further objectof the present invention to provide an oscillator having an improvedcoil or inductance element adapted to provide close couplng'between atunable grid circuit and an anode circuit ofthe oscillator device,whereby, without resulting in instability at the high frequency end ofeach range, strong oscillations are maintained over a wide operatingrange through the medium of fixed feed back coupling.

Heretofore, in a multi-range receiving system, it has been considerednecessary to provide a plurality of coils or inductances having arelatively high cost of manufacture and utilizing an appre-l ciablespace in the apparatusin which they are employed. Itis, therefore, afurther object of the present invention to provide an improved in- 55ductance unit which may be mounted in a rela- (Cl. Z50-36) tively smallspace which is more easily manufactured as a single unit having a highdegree of permanence and which provides an improved feed backcoupling'arrangement in a multi-wave band receiver or in other apparatusrequiring an oscillatory circuit tunable over a relatively wide range ina. plurality of frequency ranges. T

In carrying out the invention a pentode type oscillator device isutilized in conjunction with a single unit coil or inductance systemproviding a plurality of secondary windings adapted to be tuned throughdiffering frequency ranges as grid circuit inductances and a pluralityof primary windings closely. associated with the secondary windings onthe same coil form and adapted to be used in pairs in each tuning rangeto provide a high frequency and a low frequency primary for eachsecondary winding, the low frequency primary for a higher frequencytuning range being furtheradapted to form the high frequency primary forthe next lower frequency tuning range.

In order to provide a uniform oscillatoroutput over a wide tuning range,the low frequency primary is tuned below the tuning range of theoscillator grid circuit for the selected frequency band and the highfrequency primary is tuned above the high frequency end of the selectedfrequency band, and since the maximum feed back is obtained at primaryresonance, the use of the two primary windings tuned as above describedresultsv in a more uniform feed back or oscillator output throughout thetuning range in any band of frequencies.

The invention will, howevenbe better understood from the followingdescription when considered in connection with the accompanying drawingsand its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a schematic circuit diagram of an'oscillatorsystem embodying the Yinvention and adapted for use in conjunction witha multi-wave band receiver,

Fig. 2 is a side view, in elevation, of the inductance unit of thesystem shown in Fig. 1,

Fig. 3 is a detail view in cross section and on a greatly enlargedscale, of a portion of the inductance unit of Fig. 2, showing thearrangement of the windings thereof, and Y Figs. 4, 5 and 6 areschematic circuit diagrams showing the switching connections provided inthe system of Fig, 1 for the three differing wave band portions of theswitching means therein, and the relation of the. windings on theinductance unit for the differing frequency ranges of operation providedby the circuit of Fig. 1.

Referring to Figs. l, 2 and 3, 5 is an oscillator tube of the pentodetype having a cathode 6, an

-output anode l, a suppressor grid 8 connected with the cathode 6, ascreen grid 9 and a control grid l0.

The control grid is connected to the cathode through a grid resistor Hand is coupled to the tunable grid circuit hereinafter described,through a grid coupling capacitor I2 in the grid or high frequency leadI3 of the oscillator grid circuit, across which circuit is connected themain variable tuning capacitor l.. In the system shown, all returncircuits are made to chassis or ground indicated by the various groundconnections as designated at l5, for example. The oscillator gridcircuit is also coupled to a first detector or frequency changer tube I6through a coupling capacitor I7 and a grid lead l in connection with thefirst or inner grid i9 of an RCA @Ll or pentagrid mixer amplier, asindicated in the drawings.

Signals are applied to the detector in connection with the inner.`control grid indicated at 20 and are supplied thereto from an inputcircuit indicated generally at 2| and tunable through correspondingfrequency ranges with the oscillater by means of a second mainI variablecapacitor indicated at 22.

The grid i9 and the grid 2D are both connected to sources of biaspotential, through grid resistors indicated at 23. The intermediatefrequency output is taken from the first detector l through anintermediate frequency output transformer Z4. As. the detector does notfurther concern the present invention, further description is notbelieved to be necessary.

The oscillator circuit comprises a series of inductances 30, 3l and 32for frequency or wave band ranges which may be designated as bands C, Band A, respectively covering a frequency range in three differingcontinuously tunable bands between 1,000 k. c., for example, and 25,000k. c., the higher frequency band being the C band and B and A bandsbeing tunable through progressively lower frequency ranges.

For example, the C band may be tunable through a frequency range of from6,400 to 22,460 k. c., the B band may be tunable through a frequencyrange from 2,000 to 6,400 k. c., and the A band may cover a range offrom 1,000 to 2,000 k. c. Such frequency ranges represent any suitableapportioning of tuning range in each band, whereby the same tuningcapacitor I4 may cover the selected band by operation throughsubstantially its full tuning movement.

The secondary windings 30, 3l and 32 are each connected at one end withground as indicated at 3d and at their opposite ends are connectedthrough leads 35, 36 and 37 with switch contacts 38, 39 and 0,respectively on a wave band change switch 33 forming one unit of a gangswitch for the detector and other tuning circuits of the receiver. Theswitch unit shown is adjusted for C band operation, and in this positionthe contacts 39 and 40 are arranged to be connected to a ground contact4E through a movable insulated contact shorting element 42 whereby thesecondaries not in use are short-circuited and rendered ineffective forreducing the amplitude of oscillations set up in the selected secondary30 for the C band.

The lead 35 in connection with the contact 38 is connected with amovable insulated contact element 42 which, in the position shown,engages the contact 38 and at the same time is in ccnnection with anarcuate contact strip 44 having a terminal i5 connected with the gridlead I3 of the oscillator. The oscillator circuit is further loaded by ashunt resistor 46 connected between the grid lead i3 and ground. Theoscillator circuit SiE-lll is thus connected with the grid l0 of theoscillator for applying oscillations thereto with the switch in theposition shown.

Each of the secondary windings is provided with a suitable shunt trimmercapacitor 41 and the A band secondary 32 is further provided with afixed shunt tuning capacitor i8 for causing it to cover the desiredfrequency range. For causing the oscillator inductance in certain of thebands to "slow up the tuning of the oscillator circuit, that is, tocause the oscillator circuit tuning to change at a different rate totrack with the other tunable circuits when tuned by the variablecapacitors ld and 22, series capacitors iS and iid are provided in thegrid circuits of the two lower frequency bands. Because of the coilarrangement hereinafter described, this additional capacitor is notrequired for the high frequency C band.

To provide suitable feed back energy over a relatively wide tuning rangesuch as that required in the receiver of the present example, aplurality of primary windings or winding sections are provided in 4cioseassociation with and between the secondary windings as indicated at 55,5l and and are connected in series with cach other, as shown, in theoscillator anode output circuit indicated at SaS- 60, the latter leadextending from the lower-most coil 53 to an anode positive potentialsupply lead 6l, and the former lead serving to connect the oscillatoranode with the high frequency end of the high frequency primary section55.

The latter is preferably Wound between the turns of the high frequencysecondary winding 30 as indicated more clearly in detail in Fig. 3. twill be noted that the winding form indicated at 5i! is provided withgrooves 6l for spacing the secondary turns and holding them inpredetermined iixed spaced relation and that the winding forni issimilarly grooved between the main grooves for the secondary turns asindicated at 02, to receive the winding 55 whereby a relatively highdegree of feed back coupling is provided between the winding 55 and thewinding 30 without introducing undesirable mechanical and electricalfeatures and without an abnormally large number of feed back turns. Thecoil terminals are provided at one end of the coil form as indicated atS3, and it will be noted that all of the windings occupy a relativelysmall space on the form which is shown in Fig. 2 substantially fullsize.

n the coupling system shown, the plate and grid windings are interleavedto provide closer coupling than could be provided by placing thewindings end to end, and at the same time a relatively low degree ofcapacity coupling exists because of the dierence in sizes of theconducters.

1n many oscillator circuits, the oscillator may shift in frequency withchanges in signal input to the receiver because of changes in automaticvolurne control bias and, therefore, changes in potential on theoscillator, to such a degree that the oscillator may flutter on strongsignals. This condition is overcome by the reduction in the size of thefeed-back coil required, through interleaved windings, and also theoperation in regard to stability is improved by reducing the size of thegrid capacitor I2 with a corresponding change in the grid resistor Il,so that in the circuit shown the oscillator is stable over the fulloperating range in any frequency'band,

This follows that a xed relation is provided between the plateinductance, the mutual inductance of the plate coil to the grid coil,and the values of the grid condenser and resistor with respect to theinput resistance and impedance of the tube used as the oscillator.

For example, in the system shown, with an os-V cillator tube 5 of thetype known as the RCA 1B4, with a grid'resistor ,|I of 150,000 ohms anda grid capacitor I2 of 33 micromicrofarads, the oscillator circuit isstabilized in conjunction with the coil system shown, through the highfrequency or C band tuning range, as well as throughout the lowerfrequency tuning ranges for the B and A bands.

The switch 33 is provided with further contacts arrangeddiametricallyopposite to the contacts for the secondary windings, forchanging the connections with the primary windings and, in the presentexample, such contacts comprise f' three contacts 65, 66, and 61connected together l contact 14 and a tap point 16 between the primarywindings 55 and'56.

A second lead 11 is connected between the contact 65 and a tap point 18between the primary' windings 55 and 51, and a third lead 19 is providedbetween the contact 66 and a tap point 80 between the primary windings51 and 58. The contact 61 is connected through a lead 8| with the lowpotential lead 60 of the anode circuit.

The terminal 12 is connected to ground through a lead 82v and a primarytuning capacitor 83 in said lead for the C band while the terminal 1| isconnected to ground through a lead 84 and a primary tuning capacitor 85for the A and B bands.

The B potential supply lead 6| is also connected to the screen grid 9ofthe oscillator 5, through suitable lter means comprising a. seriesresistor 99 and by-pass capacitors ill- 92. It will also be noted thatthe oscillator cathode 6 is con nected to ground as indicated at 93.

It will be seen that a plurality of primary and secondary windings arearranged in close spaced relation to each other on a single windingform, with the primary winding sections arranged to be closely coupledwith adjacent secondary windings and the switching arrangement for thepri.- mary sections is such that as the Secondary windings 36, 3l and 32are progressively connected to the oscillator tuning capacitor and inputcircuit lead I3 for tuning through a predetermined range, the primaryVwinding connections are, at the same time, changed to conformtherewith. The various connections may be Vunderstood by consideringthat the switch 33 comprises the rotary movable elements 43'and 13engaging the lower arcuate contact stripsY 44 and 10 and 69 numerals areapplied to the same parts as inY Fig. 1.

Referring to Fig. 4, the C band connection as provided in Fig. l, isindicated, and it will readily be seen that the secondary inductance 30is connected with the oscillator grid I to provide a tunable secondarycircuit in conjunction with the tuning capacitor I4 and that the anode 1is coupled back to the secondary winding 38 through the primary winding55 and the winding 56 and that the latterris provided with the shunttuning capacitor 83.

The inductance of the winding 55 is such that it naturally tunes to afrequency above the tuning range of the secondary or grid circuit of theoscillator, while the winding 56 is tuned by the capacitor 83 slightlybelow the lowest frequency in the tuning range in the grid circuit,whereby a relatively strong and' uniform feed back of energy is providedthroughout the vtuning range oi the C band without causing theoscillator to become unstable at the high frequency end, as is normallythe case where a single winding is arranged for this purpose. v

Since the windings 51 and 58 are short circuited by the switch contactsthe-y are not included in circuit and the anode or feed back circuit isrepresented by the heavy circuit lines in connection with the anodecircuit. At the same time it will be noted that the second windings areshort circuited to ground as indicated at 35. This ground connection isthat provided in connection with the contact 4i of Fig. l.

Omitting the tube. from the connections for the purpose of simplifyingthe drawing, it will be noted in Fig. the B` band connections providefor the primary windings 56` and 51 to function in connection with thesecondary winding 3| which is connected to the grid circuit and tuningelement of the oscillator while the secondary 32 is short-circuited toground. Likewisethe primary winding section 58 is short-circuited andthe feed back circuit is indicated in heavy lines.

In this connection, the capacitor 85 is connected primary is tuned belowthe B band. The primary -winding 55 also remains in circuit and may beassumed to couple with the secondary winding 5i to a limited extent.

kSince the C band is relatively high in -frequency with respect to the Bband, the secondary winding 30 does not require short-circuiting and theprimary winding does not require elimination from the anode circuit.

Referring now to Fig. 6 for the A band connections, it will be seen thatthe primary windings 51 and 56 (are in series on either side of thesecondary winding 32 Ywhich is connected to the oscillator grid andtuning means, while the primary sections 55 'and 56 remain in circuit toaid in the coupling without in any way effecting the operation of thesystem to prevent feed back. The primary winding section 58 is tuned toa frequency below the A bandby the capacitor 85 which is now connectedin shunt with it as shown and thereby provides the low frequencyprimary, while the winding 51 provides the high frequency primary.

From the foregoing description, it will be seen that an oscillatortuning system is provided in which a series of secondary windings areselectively connectible with an oscillator grid electrode and tuningcapacitor by simple switching means and that the second-ary windings areassociated with a plurality of series connected primary sections, all ofwhich are connected in series with the oscillator anode circuit andoperated in pairs, progressively, as high and low frequency primarywindings, the low frequency primary winding of a higher frequency tuningband being utilized as the high frequency primary winding for the nextlower frequency band and that the switching operation is simplified tothe extent that it is merely necessary to progressively remove a shortcircuit from the lower frequency primary windu ings for the lowei`frequency ranges and to apply a shunt tuning capacitor to the lowfrequency primary winding for each band, which primary winding is thehigh frequency primary winding of the next lower frequency hand.

The two windings are utilized to prevent instability at the highfrequency end of the tuning range in each band and to permit strongenough feed back or oscillator output, that is, or effective feed back,at the low frequency end of the tuning range in any band., whereby thestrength of the oscillations is more uniform.

In the higher frequency tuning ranges, the double grooved windingarrangement, wherein the anode winding is included between the turns ofthe grid winding but spaced therefrom as shown in Fig. 3, for example,has the additional advantage that it cuts down the leakage and permitsenough energy transfer to provide strong oscillations at the lowfrequency end of the tuning range without permitting instability at thehigh frequency end of the tuning range when associated with the lowfrequency primary windmg.

Furthermore, in the C or highest frequency tuning range, because of theclose coupling of the primary windings, the series tracking capacitorfor the C band is not required. Because of the pentode having a screengrid and a suppressor grid connection, the coupling which wouldotherwise cancel because of capacity from grid to anode is prevented andthe oscillations are maintained throughout a wide frequency range.

I claim as my invention:

1. A multi-range tunable oscillator comprising in combination, an anodecircuit, a grid circuit, variable tuning means in said last namedcircuit, an inductance unit comprising a series of primary windingsconnected in series relation in said anode circuit, a series of gridwindings interposed between said primary windings in said unit, meansfor selectively connecting each of said grid Windings with said tuningmeans and grid circuit, means for connecting in pairs said primarywindings more adjacent to a selected grid winding, and means for causingone of said primary windings to operate as a low frequency primarywinding for a higher frequency tuning band in association with saidselected grid winding and as a high frequency primary winding inassociation with another selected grid winding for the next lowerfrequency band.

2. A multi-range tunable oscillator in accordance with claim 1, furthercharacterized by the fact that the grid circuit is coupled to thevariable tuning means and said grid windings through a couplingcapacitor having a relatively low capacity, and that a primary windingin association with one of said grid windings for the highest frequencyband is interleaved therewith, the turns of said primary winding beingwound between the turns of the grid winding and spaced there from.

3. An oscillator for a multi-waveband radio receiver, comprising incombination, an electric discharge oscillator device, an inductance unittherefor having a plurality of secondary windings adapted to be tunedthrough differing frequency ranges, means for selectively connectingeach of said windings with said device as a grid circuit inductancetherefor, a plurality of primary windings associated with and interposedbetween said secondary windings in said unit, an anode circuit for saiddevice, and means for selectively connecte ing two of saidfprimarywindings on opposite sides of a selected secondary winding, serially inpairs in each tuning range, said primary windings providing a highfrequency and a low frequency primary for each secondary winding, andmeans for causing the low frequency primary for a higher frequencytuning range to provide the high frequency primary for the next lowerfrequency tuning range.

4. n a multi-wave band oscillator for a radio receiver, a tuning systemas defined in claim 3, further characterized by the fact that in eachwave band the low' frequency primary is tuned below the tuning range ofthe secondary winding for a selected frequency band and the highfrequency primary is tuned above said tuning range, whereby a maximumfeed-back at primary resonance and a more uniform feed-back andoscillator output throughout the tuning range in any band of frequenciesis obtained.

5. An oscillator tuning system for a multi-wave band receiving systemcomprising in combination, a tuning unit comprising a series ofsecondary windings, variable tuning means selectively connectable withsaid windings, a plurality of primary windings interposed between saidsecondary Windings, an oscillator anode circuit in which said windingsare connected in series, means for operating said primary windings inpairs as high and low frequency primary windings in relation to apredetermined secondary Winding, and means for causing the low frequencyprimary winding of a higher frequency tuning band to operate as the highfrequency primary winding for the next lower frequency band.

6. An oscillator tuning system in accordance with claim 5 furthercharacterized by the fact that the lower frequency' primary windingsexclusive of one in an operative pair are short circuited, that meansare pro-vided for progressively removing the short circuit from a lowerfrequency primary winding in a pair for the next lower frequenoy range,and that a tuning capacitor and means for applying said capacitor inparallel with the lovT frequency primary winding for each band areprovided.

7. An oscillator system for a multi-wave band radio receiver comprisingin combination, an elec tric discharge oscillator device having a gridlcircuit and an anode circuit, means for variably tuning said gridcircuit, and means for adjusting said oscillator for operationthroughout a plurality of frequency ranges comprising a series ofsecondary windings tunable by said tuning means through diiferingfrequency ranges in connection with said grid circuit, selectiveswitching means for connecting each of said windings with said tuningmeans, said secondary windings being arranged in coaxial spaced relationto each other, a plurality of primary windings interposed between saidsecondary windings, said switchingV means including contacts connectedlwith said primary windings, and switching connections providing in theanode circuit a pair of primary windings as effective couplingmeans witha selected secondary winding at opposite ends thereof, means for tuningone of said primary windings to a frequency above the tuning range ofsaid secondary winding and the other of said primary windings beingresponsive to a frequency below the tuning range of said secondarywinding whereby uniform feed-back-is p-rovided for said secondarywinding throughout the tuning range thereof and said switching meansfurther including contacts connected with said primary windings'wherebythe low frequency primary winding is effective as a high frequencyprimary winding in association with a secondary winding for the lowerfrequency tuning range.

8. In a multi-wave band radio receiver, a tunable oscillator systemcomprising variable tuning means, a single tuning unit comprising aplurality of inductive windings and selective switching means connectedbetween said tuning means and said inductive windings for selectively,connecting certain of said windings in circuit with said tuning meansand others of said windings in pairs in association with a selectedwinding to provide a high and low frequency primary therefor, theprimary connection being such that a low frequency primary winding forone selected winding is effective as a high frequency primary windingfor another of said selected windings.

9. In a multi-wave band radio receiver, a tunable oscillator system asdefined in claim 8 further characterized by the fact that the primarywindings are interposed between the selectable windings for said tuningmeans and that certain of said windings are interleaved, the turns ofone winding being interposed between and spaced from the turns ofanother of said windings to provide a high degree of coupling.

10. In a multi-wave band tunable oscillator system, the combination ofan inductance unit therefor comprising a series of windings arranged inspaced coaxial relation to each other, a common winding form therefor onwhich said windings are mounted, variable tuning means, means forconnecting alternate windings selectively each with said tuning meanswhereby said windings are tunable through differing frequency ranges,and means for connecting windings at'opposite ends of a selected windingin series to provide a pair of primary windings therefor, means fortuning one of said primary windings below the fre-` quency range throughwhich the selected winding associated therewith is tunable, saidprimaryV winding being responsive to a frequency above the tuning rangeof another selectable alternate winding for a next lower frequencyrange, and means for connecting said primary winding as a high frequencyprimary winding for said lastnamed alternate winding in said next lowerfrequency tuning range.

11. In an oscillator for a battery operated receiver, an oscillatorcircuit comprising ar pluralityV of secondary windings selectivelyconnectible into the oscillator circuit, means providing a high and alow frequency primary winding in coupled relation to each of saidsecondary windings, and means for connecting the low frequency primaryfor a higher frequency secondary Vwinding in circuit to provide a highfrequency primary winding for a lower frequency secondary winding.

12. An oscillator in accordance with claim 11 further characterized bythe fact that an oscillator device is provided therein comprising anelectric discharge pentode tube having a grid circuit selectivelyconnectible with said secondary windings, and an anode circuit in serieswith said primary windings to supply oscillations thereto.

' LOREN'R. KIRKWOOD.

